The present invention relates to a wire electrode supplying device for use in a wire cut electric discharge machining apparatus.
FIG. 1 shows a conventional wire electrode supplying device disclosed, for instance, by Published Examined Japanese Patent Application No. 11111/1985. In such a device, while being restrained with a jet stream of machining solution (hereinafter referred to as "a jet stream", when applicable) a wire electrode is conveyed by a wire electrode feeding unit (not shown) from a wire guide member on the wire electrode supplying side to a wire guide member on the wire electrode receiving side which are provided on both sides of a workpiece to be machined.
In FIG. 1, reference numeral 1 designates a workpiece; 2, a machining start hole; 3, a wire electrode; 4, a wire guide on the wire electrode supplying side; 5, a wire guide on the wire electrode receiving side, 6, a jet nozzle; and 7, a jet stream.
In automatically supplying the wire electrode with the wire electrode supplying device thus constructed, the jet stream 7 is jetted from the wire guide 4 on the wire electrode supplying side, and under this condition, the wire electrode is passed through the machining start hole 2 and the wire guide 5 on the wire electrode receiving side by means of a wire electrode supplying mechanism (not shown) while being restrained by the jet stream, and is then taken up by a wire take-up mechanism (not shown) or received in a predetermined container Thus, the wire cut electric discharge machining operation can be started.
The conventional wire electrode supplying device in a wire cut electric discharge machining apparatus machine is designed as described above. Therefore, when the wire electrode comes out of the jet stream without being restrained, it becomes impossible to supply the wire electrode. FIGS. 2(a) and 2(b) are explanatory FIGURES for describing the difficulty that the wire electrode comes out of the jet stream during the wire electrode supplying operation. In FIGS. 2(a) and 2(b), those components which have been previously described with reference to FIG. 1 are therefore similarly numbered. FIG. 2(a) shows the case when the end portion of the wire electrodes comes out of the jet stream before reaching the wire guide 5 on the wire electrode receiving side. In this case, the wire electrode is not inserted into the wire guide 5, and therefore the wire electrode supplying operation must be stopped This difficulty is liable to occur especially when the wire electrode remains greatly curled.
In general, a wire electrode is wound on a wire electrode supplying bobbin before use, and therefore it remains curled to some extent. In addition, the wire electrode is curled when drawn. Furthermore, usually in the wire cut electric discharge machining apparatus pulleys and rollers are provided along the wire electrode laying path from the wire electrode supplying bobbin to the wire guide on the wire electrode receiving side, and therefore the wire electrode is additionally curled while being conveyed along the wire electrode laying path. That is, there are many causes to curl the wire electrode. Thus, the curvature and direction of curl of the wire electrode are variously changed while it is conveyed along the wire electrode supplying path.
On the other hand, the jet stream acts to make the curled wire electrode straight, and to restrain it so that it is positioned along, the central, axis of the jet stream. This restraining force is attributed to the shearing force of the fluid. The velocity of the jet stream is higher than the wire electrode supplying speed. Therefore, a fluid shearing force acts uniformly on the minute parts of the wire electrode in the wire supplying direction, and, on a point of the wire electrode, a force proportional to the distance between the point and the end of the wire electrode is exerted, thus pulling the wire electrode on the wire electrode supplying side. As a result, the curled wire electrode is made straight, and it is held at the center of the jet stream. However, it goes without saying that the restraining force of the jet stream exerted on the wire electrode is limited. According to the experiment of the present inventor, in the case where a 0.3 mm diameter brass wire is conveyed with a jet stream 1.5 mm in diameter and 5 kg f/cm.sup.2 in pressure, the wire electrode curled with a curvature radius (p) of at least 200 mm as shown in FIG. 3 is positively restrained by the jet stream, but a wire electrode curled with a curvature radius of less than 200 mm is not restrained by the jet stream, thus coming out of the latter. In the case of FIG. 2(a), after the end portion of the wire electrode has passed through the wire guide on the wire electrode receiving side, a load is developed at the wire guide to obstruct the insertion of the wire electrode, so that the wire electrode being supplied has no way to go, thus coming out of the jet stream. In this case also, the conveyance of the wire electrode must be suspended.
That is, in the conventional wire electrode supplying device, when the wire electrode is greatly curled, or when a load to obstruct the insertion of the wire electrode is developed at the wire guide on the wire electrode receiving side, the wire electrode is not restrained by the jet stream, thus coming out of the latter, as a result of which the wire electrode supplying operation must be suspended.